This invention relates to data communications effected through loop transmission lines and more particularly to a loop back control system.
In a prior art loop back system as disclosed in Japanese Patent Unexamined Publication 59-154843, after transmitting a loop back command to a slave station, the master station awaits a carrier wave transmitted from the interrogated slave station until a predetermined interval of time calculated on the basis of a maximum network configuration has elapsed and then it decides either success of loop back if the master station receives the carrier wave or failure of loop back unless the master station receives the carrier wave, raising a problem that a formation of loop back is time-consuming.